MIRROR AND MIRROR SUBSTRATE WITH HIGH ASPECT RATIO, AND METHOD AND MEANS FOR PRODUCING SUCH A MIRROR SUBSTRATE

A mirror, a mirror substrate, a method for producing are provided. The mirror substrate is made of a material having a coefficient of mean linear thermal expansion of less than or equal to 1*10−6/K. The mirror substrate includes at least one feature selected from a group consisting of: a ratio of a lateral dimension to a maximum thickness of at least 100, a ratio of the lateral dimension to the maximum thickness of at least 150, a ratio of the lateral dimension to the maximum thickness of at least 200, a ratio of the lateral dimension to the maximum thickness of at least 300, a weight per unit area of 100 kg/m2 or less, a weight per unit area of 50 kg/m2 or less, a weight per unit area of 30 kg/m2 or less, a weight per unit area of 15 kg/m2 or less, a mirror surface with a roughness (Ra) of at most 3.5 μm, and a mirror surface with a roughness (Ra) of less than 1.2 μm.